Thursday, 29 May 2014

Pulsing LED and the PUT Transistor (2N6027)

I’ve been playing with pulsing/breathing LED circuits for a little while, you may think that I’m a little obsessed. Maybe.
I bought Charles Platt’s Make: Electronics book from Amazon and, much to my delight, I found a circuit described there that does the pulsing/breathing thing. I then set out to buy the parts needed to make this circuit. Some contributors on the Internet have scoffed at this circuit because the transistor (the programmable unijunction transistor) is woefully old and difficult to obtain. That’s as maybe, but I bought 25 of these on eBay for $6.71 AUD (or $0.27 each if you prefer) from the eBay vendor dpi4parts. It took all of 12 days for the delivery to arrive. That didn’t seem too hard to me.
The alternative that has been suggested on the Internet (from many sources) is to use a Darlington pair. Meh … I’ll use the 2N6027, thanks.
I’ve re-rendered the circuit here in Fritzing:
Fritzing PUT Pulsing LED_bb_thumb[1]
Feel free to use my rendition.
And here is the exported PCB from Fritzing too.
Fritzing PUT Pulsing LED_pcb_thumb[3]
I then transfer printed and etched the board, drilled it out and populated it.
Populated Board - Top_thumb[1]
Top view of the populated board.
Populated Board - Bottom_thumb[2]
Bottom view, showing my lovely soldering ;p Yah … it’s neat enough.
Populated Board - Powered_thumb[1]
And here it is, powered up. When the circuit is connected to power, it takes a little while for the capacitors to “fill up” and start to cycle. Also, this circuit (as mentioned in the book) requires 9V power. If you use, say, 5V, the LED will eventually light up, but it won’t cycle. That’s got to be my only gripe about this circuit.
When it does cycle, it should look something like:
PUT Pulsing LED
I’ve used a 220µF Capacitor for C1 rather than the 100µF that Charles Platt has in his book. The choice is entirely aesthetic.
The PCB is 3.75 cm long x 2 cm wide x 1.5 cm high.
This circuit has a larger footprint than the NE555 based circuit and costs slightly more. I calculated a parts cost at $0.69 AUD for this circuit versus the $0.60 AUD for the NE555 based circuit. Go figure, I would have thought that the costs were the other way around. But then, the NE555 IC only costs $0.20 compared to the $0.27 for the PUT transistor. I guess the other factor to consider is that the NE555 based circuit runs on 5V and the components are easier to acquire.
I made a small batch (3) PCB for this, so I guess I’m going to find a use for them.

Monday, 26 May 2014

Happy Days! – New eBay Order Arrives

Today, I received three of my eBay orders. The 0805 120Ω resistors, the 0805 white LED and the MAX7219ENG LED control chips.

Picture 49

This is the LED from the bottom. the tiny arrow indicates the anode (positive) and cathode (negative) side of the LED. The arrow points toward the positive, just as it does in the schematic for an LED.

Picture 50

I took one of the LED out of the packaging and gave it a quick test (multimeter on continuity test) to make sure that the LED was “live”.

Picture 51

This means, simply to touch the negative probe of the multimeter to the cathode end of the LED and the positive probe to the anode end. For those of you with a classical education “Fiat Lux” … for the rest of us “Let there be light”.

Picture 52

The resistors are the same length as the LED, but they are wider. The markings are right, I haven’t tested them yet … but I am confident that these resistors are OK … maybe that’s a little optimistic of me but, whatever, they only cost me peanuts .

I got 50 x 120Ω 0805 resistors for $1.33 AUD from citybestbuy, the 50 x 0805 LED (Super Bright White) were $2.41 from yankee_electronic. The 10 x MAX7219ENG I bought at auction from gc_supermarket for $5.34.

These orders arrived < 13 days from China to Tasmania, so I am a happy eBayer today.I should really have bought 100 of each of the resistors and LED, but then, I really only bought these so that I could try my hand at hand soldering SMD components. If I think that I can handle this form factor, then I’ll get some more or I may have to get the next size up. As I have said before, my eyes aren’t all that good any more.

I knew that the 0805 SMD were small, I knew their size because I checked and rechecked various online sources so that I’d have a good idea of their package size, but really? Now that I actually have some actual 0805 in my hand … they are VERY small indeed!

I’m going to try to whip up a simple 4 x 4 LED PCB and have a go. Not tonight, though.

Thursday, 22 May 2014

Simple NE555 Pulsing LED – In A Box

Now that I’ve made the pulsing LED and soldered it all up on perfboard, I want to make an enclosure for it, ideally, one that diffuses the light and looks cool.
I have some 0.75 mm white PVC sheet at home that I’ve had for years and years (I used to use this for making table-top war-gaming scenery). The PVC sheet should be sturdy enough when it is glued into a solid shape and thin enough to allow light through and to diffuse it.
What I’m aiming for is, simply, a box to put the board in. I’ll probably use some hot melt glue to adhere the board to the PVC and I’ll cut a hole through one of the boxes walls to pass the power connector through.
NE555 Pulsing Box
When the circuit is powered, the light will pulse and the PVC will spread the light through it’s walls creating a glowing, pulsing box.
Last night, I cut the PVC and glued up all but one side of the enclosure (I’ve left the side with the power hole unglued) and I gave it a test run. The result was fairly pleasing … but quite plain.
I’m confident that the enclosure will do what I want it to do (glow and pulse). So, now I’m going to think about how to make it look Lovecraftian. The obvious approach is to cut up more PVC to make some faux pierce-work pieces to apply to the outside of the box. Alternatively, I could design and print out some black and white imagery and glue it inside the box. The thinking there is that the parts of the image that are black would prevent the light passing through the enclosure. Maybe a combination of the two.

Pulsing red LED in a custom PVC box. Now it just needs decorating.

I’ll return to this thread at a later date. I need to do some design work on the box to make it more worthy of being called Steampunk. For now … it’s just a glowing, pulsing box.

Wednesday, 21 May 2014

Simple NE555 Pulsing LED Perfboard

Following on from the previous post (Breadboard Version), I’ve soldered the circuit up on a small bit of perfboard (about 25mm x 35mm).
For this build, I’ve mostly used the bent leads of the components to join the bits together, along with a minimum of jumper leads.
Self Leads
I’ve placed the labels for the components as close to the component as possible … this is the under-side of the board.
As with the previous post … here is the top view of the board.
Picture 45Picture 46Picture 47Picture 48
My biggest hassle with this circuit was that I forgot to link the input voltage to the collector of the transistor. I had a bit of a swear at myself for that, after I went over the circuit with my multimeter to give it a continuity test. I had rushed the build and I was totally ready to swear some more.
This version returns to the original design with a 100 uF electrolytic capacitor. I ran the solderless version for a while last night and decided that 100 uF was better. Oh well, you live and you learn.
Perfboard version of the Simple NE555 Pulsing LED
The video just shows the circuit with power, going through a couple of cycles.

Tuesday, 20 May 2014

Simple NE555 Pulsing LED Breadboard

Here’s a simple pulsing LED circuit that I found online (by MrBeta)
I’ve made some virtually unnoticeable changes to how Mr Beta describes the circuit on his instructable, however, I hope that the photographs and video are more clear. I have had some trouble with this circuit and I’ve usually abandoned it after a couple of minutes.
This time, however, I persisted and worked it out.
Initially, I was after, pretty much exactly, this effect. A simple pulsing LED. The idea was to use this circuit within a Steam Punk prop (such as in a ray-gun). This component was going to be part of more LED jiggery pokery and I had moved on to achieving something similar as part of an overall Arduino controlled LED array (multiple LED doing various things simultaneously). Anyway, I’ve been thinking more about this circuit and, since I have a bunch of SO8 555 chips, I’d work on making this with SMT rather than through hole … another planned exercise for when my SMT LED and Resistors arrive (oh, and I’ll have to get some SMT transistors and capacitors).
The project requires:
  • NE555
  • 33k ohm resistor
  • 470 ohm resistor
  • 33 uF capacitor
  • LED (I’ve used spooky green)
  • 2N2222 NPN transistor
I’ve put this together on a solderless breadboard and photographed it from every angle and put some labels on the pictures to make it easier to reproduce.
Picture 42Picture 44
Picture 45Picture 43
And here is a video of the pulse. MrBeta used a 100uF capacitor, but that was a little bit too slow for what I wanted. The 33 uF capacitor gave me a much more satisfactory cycle.
Simple Ne555 pulsing LED
Anyway, that’s it for now. have fun!

Wednesday, 7 May 2014

MAX7219 and the Arduino

I received my 8x8 LED Matrix with the MAXIM7219 chip that I bought on eBay.
Picture 40
and then I proceeded to try and get it up and running with the Arduino UNO that I have.
A quick search on the Internet didn’t really help me very much, at first. But then I found an Instructable that was actually useful, it makes use of the MakeSpace LEDControl library (LedControlMS.h). There were some other little gotchas along the way too. Like, how the hell do you install a user contributed library into the Arduino IDE? Fortunately, there is a guide on libraries on the Arduino website, so I was able to get the library and install it.
The library comes with an example sketch, so I used that as a starting point and started to scratch around in the code to see what I could do.
Picture 41
The example contains three very useful lines of comment:
pin 12 is connected to the DataIn
pin 11 is connected to the CLK
pin 10 is connected to LOAD
Apart from that, you connect GND on the board to GND on the Arduino and VCC on the board to 5V on the Arduino, compile and load and you are away!
The LED Matrix running after a little tinkering with the sketch.
The upshot is, the use of an LED Display Matrix is very easy. If I need to have a display happening on any of my electronic projects, I know what I’m going to use.
Also, I’ve had a look around the Internet for DIY LED Display Matrixes, and there are some projects out there that I might very well undertake for myself and see how far I can push it. One or two projects out there using tri-colour LED, they look pretty cool.

Tuesday, 6 May 2014

LED Desk Light – 4 x 5 Matrix – PCB – Part 2

I’ve completed the etch of my 4 x 5 LED Matrix PCB and there are two gaps in the circuit.
The trace gaps are marked with red boxes. The gap in the negative trace was found using my multimeter using the continuity test function and verified visually. The gap in the connection from the LED cathode to the resistor can be plainly seen. This gap was where there was a missing trace in the laser printout that I “fixed” using the permanent marker, clearly, the marker wasn’t permanent enough. I think that it would have been OK if I had gone over that resist line a couple of times. Well, that’s a good lesson for me.
To fix the break, I intend to over-solder the negative trace gap and to solder in a jumper on LED 8.
PCB_Etched with LED numbers
My next task will be to drill and solder in the power at the bottom right of the PCB and then connect LED 1 along with it’s resistor. That should be proof enough that the trace is working.
After that, it will be a matter of plodding on with the remaining LED and resistors.
Now that I’ve populated the PCB and given it power … I can see that there were some other problems with the traces. LED 11 and 16 are non-responsive. When I test them with the multimeter, they respond, but not when the board is powered. Oh well … it’s a prototype.
Picture 39
Picture 38
With that done … I’m going to try another board and see if I can work out the bugs in the traces before I populate it. What a pain in the butt.
I’m going to order some SMD resistors and LED and get on to the SMD version of the 4 x 5 LED Light.

Monday, 5 May 2014

LED Desk Light – 4 x 5 Matrix – PCB – Part 1

Now that I have completed the perf-board prototype of the 4 x 5 LED matrix, it’s time to start work on the printed circuit board version.
I’ve laid the board out, pretty much the same as for the perf-board version, although I want to try something slightly different with the positive and negative traces so that I don’t have to use any jumper leads to do the column joins.
The new layout is below
Fritzing 5 x 4 LED Array_etch_copper_bottom_mirror_thumb[1]
The above is the bottom layout in mirror reverse. You can see that all of the positive traces connect at the bottom of the columns and the negative traces connect at the top. It’s no longer simply a bent parallel line of LED, but an integrated parallel circuit. I think that this layout will work, theoretically, but I’m not sure if it will, practically. Note the missing trace in the middle of the board!
I also found out that I can make Fritzing lay out the resistors in a horizontal alignment by changing the pin spacing … simple, really, and something the Fritzing team already though of.
Fritzing Resistor_thumb[1]
This makes the Fritzing layout very similar to the perf-board layout.
I’ve printed the bottom layer out and transferred it to my single layer F4 copper clad board.
The transfer is OK
Picture 33_thumb[1]
although it is a little bit … bitty. I still need to print this out on some decent paper. However, with the traces “mostly” there, I can go over the circuit with my trusty permanent marker.
Picture 37_thumb[1]
Using a ruler and reading glasses, it becomes better.
The pads are probably a little bit blobby, but that’s OK too. This is still just a prototype. I think I need a finer permanent marker … or better eyes.
From here, I’m going to etch the board. But that’s a job for tomorrow night.

Thursday, 1 May 2014

LED Desk Light – n x n matrix – Je suis fini

Yay … I’ve completed the LED Desk Light 5 x 4 matrix!
That wasn’t so hard. Well … now that I’m sporting a bright shiny new pair of +3 reading glasses (for the princely sum of $15AUD).
The reading glasses made the soldering very easy. Much easier than the desk magnifying glass. I was finding that the focal length of the magnifying glass was too short, and so, the depth of field/operating space was much too limited. The reading glasses give me a much better nose to soldering iron length.
Anyway, enough of me whining about my aging eyes and on to the show and tell.
The main action takes place on the underside of the perf-board.
Picture 30
As I described in the previous post (here) the matrix is really just one parallel run of LED and resistors. I’ve linked the LED anodes with red jumpers and the resistors with black jumpers. The 2 pin header is at the top right of the perf-board and the series runs from there to the left, then down and to the right, down and to blah, blah, blah … as seen in the following image.
series direction
Soldering the jumpers on was a little bit of a pain, the distance between the leads is fairly small so a) stripping the wire was annoying and b) holding the jumpers in place with alligator clips was a pain. Still … all done now, I can move on.
Picture 31
The top side of the perf-board is much more attractive. All of those 5mm LED and their resistors all aligned nicely in a grid. Very nice and uniform. Just to the right, you can see the 2 pin header and the 2 pin Dupont connector that I made up for the 5.7V AC Adaptor. I’m pretty pleased with the adaptor modification. I may have to do a little re-work on the circuit to include a switch, but that can come later. You can also see how the resistors worked out using the paddle pop stick as a bending jig, and also in the horizontal alignment.
Finally, you want to see it all lit up, right? Well, here it is.
Picture 32
All lit up like candles on a birthday cake. It is quite bright but only has a 25o viewing angle. I’m thinking about making a project box with an opaque white cover to work as a diffuser. That should work.. I also need to think about how to mount the light on a stand so that it casts it’s light down (or up if I want). Again … later.
All up, I’m happy with the prototype and I’m going to start planning the SMT edition of the light. All I need to do is find some suitable (and cheap) components on eBay. On reflection, I think I’ll use the 0805 rather than the 0603 it’s enough of a difference in size to make it easier on me and still small enough to make it worth while.
Oh and … in case you are wondering, the perf-board is 50 x 70mm in size.

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